Method for producing 2,3,5,6-tetrahalogen-xylylidene compounds

ABSTRACT

The invention relates to a process for preparing 2,3,5,6-tetrahaloxylylidene compounds of formula (I)  
                 
 
     where each Hal is independently fluorine or chlorine, and X is fluorine, chlorine, bromine, —O—R, or —O—C(═O)R, where R is hydrogen, a straight-chain or branched C 1 -C 12 -alkyl- or a C 6 -C 14 -aryl radical, by reacting 2,3,5,6-tetrahaloxylylidenediamines of formula (II)  
                 
 
     with an alkyl nitrite and/or nitrous acid in HX as a solvent.

[0001] The present invention relates to the preparation of2,3,5,6-tetrahaloxylylidene compounds by diazotization of2,3,5,6-tetrahaloxylylidenediamine.

[0002] 2,3,5,6-Tetrahaloxylylidene compounds are known to those skilledin the art as important intermediates, for example for preparing activepharmaceutical or agrochemical ingredients such as insecticides.

[0003] The preparation of 2,3,5,6-tetrahaloxylylidenediols, their estersand ethers is only possible by few prior art methods: for example,GB-A-21 27 013 describes the reduction of tetrafluoroterephthalylchloride using sodium borohydride to give tetrafluoroxylylidenediol andalso the subsequent esterification using acetyl chloride to givetetrafluoroterephthalyl acetate.

[0004] EP-A-0 152 174 further discloses a complicated reaction sequencestarting from 2,3,5,6-tetrafluorotoluene which involves metallation,methylation, bromination, substitution of the xylylidene dibromide bypotassium acetate and hydrolysis to give2,3,5,6-tetrahaloxylylidenediol.

[0005] The preparation of tetrahaloxylylidenediamine by hydrogenation oftetrahaloterephthalonitrile using a hydrogenation catalyst based onrhodium, palladium, ruthenium, nickel, cobalt or platinum and also inthe presence of acids is described in EP-A-099 622.

[0006] The conversion of 2,3,5,6-tetrahaloxylylidenediamine to2,3,5,6-tetrahaloxylylidene compounds with cleavage of the N—C bond hashitherto not been described.

[0007] It is an object of the present invention to provide a processwhich facilitates industrial preparation of 2,3,5,6-tetrahaloxylylidenecompounds with high space-time yields from simple precursors.

[0008] The invention provides a process for preparing2,3,5,6-tetrahaloxylylidene compounds of the general formula (I)

[0009] where each Hal, which may be the same or different, is fluorineor chlorine and X is fluorine, chlorine, bromine, —O—R or —O—-C(═O)R,where R is hydrogen, a straight-chain or branched C₁-C₁₂-alkyl- or aC₆-C₁₄-aryl radical,

[0010] by reacting 2,3,5,6-tetrahaloxylylidenediaimines of the generalformula (II)

[0011] where Hal is as defined for the general formula (I),

[0012] characterized in that compounds of the general formula (II) arereacted with alkyl nitrites and/or nitrous acid in HX as a solvent,where X in HX is as defined for the general formula (I).

[0013] In the process according to the invention, the substituent X inthe general formula (I) and also in HX is preferably fluorine, hydroxyl,OR or —O—C(═O)R, where R is hydrogen or a straight-chain or branchedC₁-C₆, in particular a C₁-C₄-alkyl radical. More preferably, the solventHX used is water, so that the compounds obtained of the general formula(I) are 2,3,5,6-tetrahaloxylylidenediols.

[0014] The diazotization of the 2,3,5,6-tetrahaloxylylidenediamines ofthe formula (II) is effected in the process according to the inventionin the presence of alkyl nitrites and/or nitrous acid. Useful alkylnitrites include C₁-C₁₀-alkyl nitrites, and isoamyl, ethyl or methylnitrite are preferably used, and methyl nitrite is most preferably used.Instead of or in addition to the alkyl nitrite, nitrous acid may also beused. This can also be prepared in situ from an alkali metal nitriteand/or an alkaline earth metal nitrite and a mineral acid and/or acarboxylic acid. In this case, the alkali metal nitrite and/or alkalineearth metal nitrite is preferably calcium nitrite, magnesium nitrite,sodium nitrite or potassium nitrite, and the mineral acid is preferablysulfuric acid, hydrochloric acid, hydrofluoric acid, chlorosulfonicacid, fluorosulfonic acid or phosphoric acid. The carboxylic acid may,for example, be formic acid, acetic acid, propionic acid or benzoicacid.

[0015] A preferred embodiment of the process according to the inventionemploys, in addition to the solvent HX, one or more other inertsolvents. Useful other inert solvents for the process according to theinvention include C₃-C₃₀-, preferably C₆-C₁₂-alkanes, C₅-C₃₀-,preferably C₆-C₁₂-cycloalkanes, C₆-C₂₀-, preferably C₆-C₁₈-aromatics,C₃-C₃₀-esters and C₃-C₃₀-ethers. Preference is given to using hexane,heptane, petroleum ether, cyclohexane, decalin, benzene, toluene, thexylenes, chlorobenzene, dichlorobenzene, trichlorobenzene, ethylacetate, butyl acetate, diethyl ether, tetrahydrofuran or diphenylether.

[0016] It will also be advantageous to adjust the pH of the reactionmixture by addition of mineral acids and/or carboxylic acids to a valueof from 0 to 9, preferably from 2 to 7 and more preferably from 3 to 5.The mineral and carboxylic acids used may be the compounds alreadymentioned above for the in situ preparation of nitrous acid.

[0017] The process according to the invention is operated attemperatures of from 0 to 100° C., preferably from 30 to 60° C.

[0018] The pressure during the diazotization is from 0.2 to 200 bar,preferably from 0.5 to 50 bar and more preferably from 1 to 10 bar.

[0019] The molar ratio of the compounds of the formula (II) to the alkylnitrite and/or to nitrous acid is from 1:(2-10), preferably 1:(2-4). Thereaction solution has a reactant content of from 1 to 50% by weight,preferably from 5 to 25% by weight.

[0020] The process according to the invention may be operated incustomary reactors, and batchwise, semicontinuously or continuously. Theexact industrial embodiment depends on the process parameters and may bedetermined easily by those skilled in the art.

[0021] The starting materials for the process according to the inventionare compounds of the formula (II), which are preferably obtained byhydrogenation of the appropriate tetrahaloterephthalonitriles.

[0022] A preferred embodiment involves operating the process accordingto the invention in such a way that the compounds of the formula (II)are prepared by hydrogenation of compounds of the general formula (III)

[0023] where Hal and X are as defined for the general formula (I),

[0024] in the presence of a hydrogenation catalyst and a solvent HX.

[0025] Useful hydrogenation catalysts include all customary and knowncatalysts for the hydrogenation of nitrites. In particular, catalystsbased on elements of transition group VIII of the periodic table haveproven useful. Preference is given to using hydrogenation catalystsbased on rhodium, palladium, ruthenium, nickel, cobalt or platinum, andparticular preference to using palladium catalysts.

[0026] Hydrogenation is also carried out in the presence of one or moresolvents HX, where X is as defined for the formula (I). Other inertsolvents may optionally also be present. The reaction temperature of thehydrogenation is from −30 to +60° C., preferably from 0 to 30° C., andthe pressure from 3 to 300 bar, preferably from 10 to 100 bar.Preference is given to hydrogenating in the presence of mineral acidsand/or carboxylic acids. The mineral acids and carboxylic acids used maybe those already mentioned for the process according to the invention.

[0027] A particularly advantageous process variant is characterized bythe compound of the formula (II) obtained by hydrogenation being freedfrom the hydrogenation catalyst by filtration and, if necessary afterdistillative removal of troublesome solvent, introduced directly to thediazotization without an intervening isolation. This may be carried outby using the reaction solution obtained after hydrogenation as aninitial charge and adding the diazotizing reagent alkyl nitrite and/ornitrous acid, or vice versa.

[0028] The process according to the invention delivers the desired2,3,5,6-tetrahaloxylylidene compounds in high purity and with highspace-time yield via simple process steps.

EXAMPLES Example 1 Preparation of 2,3,5,6-tetrafluoroxylylidenediamineas a Sulfuric Acid Solution

[0029] 1 249.5 g (6.24 mol) of 2,3,5,6-tetrafluoroterephthalonitrile areinitially charged to a 101 autoclave together with 750 ml of methanol, 5250 ml of water, 1 050 g of concentrated sulfuric acid and 75 g of a 5%palladium-carbon catalyst and hydrogenated at 30° C. and 30 bar ofhydrogen pressure until constant pressure is obtained. The catalyst isfiltered off. The methanol is then distilled off again at 80 to 90° C.and 350 mbar. 6 690 g of a sulfuric acid solution are obtained, whichaccording to GC analysis (external standard) contains 1 197.2 g (5.75mol) of tetrafluoroxylylidenediamine (92% yield).

Example 2 Preparation of 2,3,5,6-tetrafluoroxylylidenediol

[0030] 3 200 g (2.87 mol of compound) of a tetrafluoroxylylidenediaminehydrosulfate solution prepared as above are adjusted to pH 4 using 868 gof 20% sodium hydroxide solution. The reaction mixture is heated to 80to 90° C. and 981 g of a 40% sodium nitrite solution are added dropwisewithin 4 h. Simultaneously, the pH of the solution is held between 3 and5 with the aid of 127 g of 30% sulfuric acid. When no more gas isformed, the reaction batch is extracted twice with 750 ml of ethylacetate and the organic phase is then concentrated under reducedpressure. 456 g (2.17 mol) of 2,3,5,6-tetrafluoroxylylidenediol areobtained in a purity of 74.5% and a yield of 76%.

1. A process for preparing 2,3,5,6-tetrahaloxylylidene compounds of thegeneral formula (I)

where each Hal, which may be the same or different, is fluorine orchlorine and X is fluorine, chlorine, bromine, —O—R or —O—C(═O)R, whereR is hydrogen, a straight-chain or branched C₁-C₁₂-alkyl- or aC₆-C₁₄-aryl radical, by reacting 2,3,5,6-tetrahaloxylylidenediamines ofthe general formula (II)

where hal is as defined for the general formula (I), characterized inthat compounds of the general formula (II) are reacted with alkylnitrites and/or nitrous acid in HX as a solvent, where X is as definedfor the general formula (I):
 2. The process as claimed in claim 1,characterized in that X in the general formula (I) or HX is fluorine,hydroxyl, OR or —O—C(═O)R, where R is hydrogen or C₁-C₆-, and preferablyC₁-C₄-alkyl.
 3. The process as claimed in claim 1 or 2, characterized inthat the alkyl nitrites used are C₁-C₁₀-alkyl nitrites, preferablyisoamyl, ethyl or methyl nitrite.
 4. The process as claimed in one ormore of claims 1 to 3, characterized in that, instead of or in additionto the alkyl nitrite, nitrous acid is used.
 5. The process as claimed inclaim 4, characterized in that the nitrous acid is prepared in situ froman alkali metal nitrite and/or an alkaline earth metal nitrite and amineral acid and/or a carboxylic acid.
 6. The process as claimed inclaim 5, characterized in that the alkali metal nitrite or alkalineearth metal nitrite used is calcium nitrite, magnesium nitrite, sodiumnitrite or potassium nitrite, and the mineral acid used is sulfuricacid, hydrochloric acid, hydrofluoric acid, chlorosulfonic acid,fluorosulfonic acid or phosphoric acid and/or the carboxylic acid usedis formic acid, acetic acid, propionic acid or benzoic acid.
 7. Theprocess as claimed in one or more of claims 1 to 6, characterized inthat operation is effected in the presence of water using HX as solvent.8. The process as claimed in one or more of claims 1 to 7, characterizedin that the pH of the reaction mixture is adjusted by addition of themineral acids and/or carboxylic acids mentioned in claim 6 to a value offrom 0 to 9, preferably from 2 to 7 and more preferably from 3 to
 5. 9.The process as claimed in one or more of claims 1 to 8, characterized inthat operation is effected at temperatures of from 0 to 100° C.,preferably from 30 to 60° C., and a pressure of from 0.2 to 200 bar,preferably from 0.5 to 50 bar and more preferably from 1 to 10 bar. 10.The process as claimed in one or more of claims 1-9, characterized inthat the compounds of the general formula (II) are obtained byhydrogenation of compounds of the general formula (III) in the presenceof a hydrogenation catalyst and a solvent HX,

where Hal and X are as defined for the general formula (I).
 11. Theprocess as claimed in claim 10, characterized in that hydrogenationcatalysts based on elements of transition group VIII of the periodictable, preferably based on rhodium, palladium, ruthenium, nickel, cobaltor platinum, are used.
 12. The process as claimed in claim 10 or 11,characterized in that the hydrogenation is carried out in the presenceof one or more solvents HX, where X is as defined for the formula (I),the reaction temperature of the hydrogenation is from −30 to +60° C.,preferably from 0 to 30° C., and the pressure is from 3 to 300 bar,preferably from 10 to 100 bar.
 13. The process as claimed in one or moreof claims 10 to 12, characterized in that the compound of the formula(II) obtained by hydrogenation is freed from the hydrogenation catalystby filtration and, if necessary after distillative removal of thesolvent, is introduced directly to the process as claimed in one or moreof claims 1 to 8.